The present invention relates to a novel seam which is intended for use in endless woven type papermakers fabrics, more particularly for base fabrics for press felts. The majority of press felts in use today include base fabrics which are formed either by spirally winding and joining relatively narrow strips of flat woven cloth so as to build up a desired fabric width, flat weaving the base fabric to the desired full width and length of the finished fabric, or by the so-called endless weaving process. Endless woven type base fabrics for press felts are well known in the papermaking industry and have been in widespread use for many years. Regardless of the type of base fabric construction that is employed, it is desirable in certain instances to be able to incorporate into the base fabric means for seaming the fabric to facilitate its installation on the papermaking machine for which it is intended. Approximately 40% of press fabrics manufactured at present contain a seam.
In the endless weaving process, the fabric is woven such that two layers are formed simultaneously, in a manner similar to a tubular garment such as a tube sock. During weaving, a continuous weft yarn is interwoven with the warp yarns somewhat like a spiral, but when the fabric is installed on the papermaking machine, the fabric is rotated such that the weft yarns are oriented in the machine direction (MD) of the fabric, and the warp yarns in the loom become oriented in the cross-machine direction (CD) of the fabric. The endless weaving process produces a fabric whose length is twice the width of the reed on the loom. Although this process uses a single continuous weft yarn, it is known and understood to refer to “weft yarns” as indicative of segments of the weft yarn and their paths in one of the fabric layers, and references herein to “weft yarns” should be understood as having this meaning.
When a seamed endless woven fabric is to be manufactured, the first layer of cloth is anchored at one side of the loom by its weft yarns to a so-called forming wire, so as to form seaming loops; at the opposite side of the loom, the fabric is folded over on itself and the weft yarns are brought back to the forming wire. The manner of weaving the continuous weft yarn across the body of the fabric, around the forming wire and back into the fabric results in a fabric having at least two layers of weft yarns in its construction. In this manner, an endless structure is produced which includes the seam already formed during the weaving process. These manufacturing techniques are well known to those of skill in the art and variants thereto have been described in the patent literature, for example in U.S. Pat. No. 4,896,702 to Crook, U.S. Pat. No. 5,531,251 to Rydin, and U.S. Pat. No. 5,732,749 to Fargeout. It is also known from U.S. Pat. No. 6,508,278 to Kornett, in a system requiring three sets of CD yarns, to modify one or more of the yarn denier, yarn spacing or weave pattern of the yarns in the fabric adjacent to the seam so as to improve the properties of the fabric in that area to be more consistent with the properties of the remainder of the fabric to reduce sheet marking.
However, a problem common to all of the prior art pin seam constructions has been the ability to attain acceptable uniformity of the seaming loops to facilitate installation on the papermaking machine, after the forming wire is removed, and subsequently replaced by a pintle to secure the seam for operation. Theoretically, the manufacturing process should produce uniform seaming loops with little variation in the orientation, size and shape, but this is seldom the case in actual fact. As a result, the seam loops are difficult to mesh together in order to provide a clear and open channel for the pintle.
Various constructions have been suggested, for example in U.S. Pat. No. 6,000,441 and U.S. Pat. No. 6,079,454, both to Lee et al., which have attempted to address the problem of producing more uniform seaming loops. However, none have been entirely successful to date.